1. Field of the Invention
The invention relates generally to an apparatus for measuring a slant angle in a solid immersion lens, and more particularly to, an apparatus for measuring a slant angle in a solid immersion lens capable of measuring an inclination of the solid immersion lens which is a core element in a near-field optical data storage head for storing/reading data using the immersion lens.
2. Description of the Prior Art
A focusing control unit in a near-field data storage unit using a conventional solid immersion lens obtains a focus signal by comparing the light internally totally reflected from the plane of the solid immersion lens and the intensity of the reference light. In case that the solid immersion lens is inclined against an optical axis, however, it may occur an error in detected focus signals since the location where the internally total reflection occurs is changed. Therefore, it is essential to detect whether the solid immersion lens is inclined against the optical axis and then the signal detection against the inclination and the focus signal should be detected.
FIG. 1 shows a focusing control unit in a near-field data storage head using a solid immersion lens.
Referring now to FIG. 1, a focusing control unit in a near-field data storage unit using an solid immersion lens includes a solid immersion lens 104, a polarized light splitter 101 for generating a reference light 111 and a signal light 112 from an incident light 110, a first photodetector 107 for measuring the intensity of the reference light 111, and a second photodetector 109 for measuring the intensity of the signal light 112 totally reflected from an internal side of the solid immersion lens 104.
Further, a first focusing lens 106 is installed between the polarized light splitter 101 and a first photodetector 107, and a second focusing lens 108 is also installed between the polarized light splitter 101 and the second photodetector 109. A xc2xc wave plate 102 and a third focusing lens 103 are sequentially installed between the polarized light splitter 101 and the solid immersion lens 104.
If the incident light 110 is incident to the polarized light splitter 101, the polarized light splitter 101 generates the reference light 111 and the signal light 112. The reference light 111 is incident to the first photodetector 107 via the first focusing lens 106 and the first photodetector 107 detects the intensity of the reference light 111. Meanwhile, the signal light 112 is incident to the solid immersion lens 104 via the xc2xc wave plate 102 and the third focusing lens 103. The incident signal light 112 is then totally reflected within the solid immersion lens 104 and then returns to the polarized light splitter 101 via the third focusing lens 103 and the xc2xc wave plate 102. The totally reflected signal light 112a is incident to the second photodetector 109 via the second focusing lens 108 and the second photodetector 109 detects the intensity of the totally reflected signal light 112a. 
As such, the reference light 111 and the totally reflected signal light 112a are compared to produce a focus signal. At this time, the value of the focus signal can be obtained based on below mathematical equation 1:
x=p/qxe2x80x83xe2x80x83[Equation 1]
where p indicates the intensity of the reference light and q indicates the intensity of the totally reflected signal light.
However, if the solid immersion lens 104 is inclined against to the optical axis, the location of the focus is varied and it thus occurs an error in an erroneous focus signal.
The present invention is contrived to solve the above problems and an object of the present invention is to provide an apparatus for measuring a slant angle in an solid immersion lens capable of preventing generation of an error in the focus signal by statistically measuring the inclination degree of the solid immersion lens based on the bottom using the principle of an autocollimator.
In order to accomplish the above-mentioned object, an apparatus for measuring a slant angle in an solid immersion lens according to the present invention, is characterized in that it comprises an optical generating unit for generating light to be incident to a solid immersion lens made of a hemispherical shape; a focusing lens for focusing the light reflected from a reflecting face below the solid immersion lens; and a detecting means for measuring the inclination of the solid immersion lens depending on a focus of the light focused by the focusing lens.
Further, the apparatus for measuring the slant angle in the solid immersion lens further includes an optical splitter for making incident the light generated from the optical generating unit to the focusing lens and making parallel the light within the solid immersion lens.